It's kinda amusing copyright always seems to attract discussions about authors rights. It was never about author or their rights. It was and is a set of rules that allow money to be made by publishing books and songs. Authors have a role in that, but so do publishers.

Turns out most authors and publishers suck at their respective jobs. Most books produced by authors are things nobody wants to read. If a publisher's job is defined to be finding works the public likes, they suck at it too. Instead they just publish lots of stuff, mostly at a loss. They make their money from the occasional hit. But only way they can make money from it is if they have a monopoly over publishing it for a while - which is exactly what copyright gives them. Looked at in another way, this "publish lots of stuff and see what sticks" is the way our society discovers what new works are popular. And copyright funds it.

If you take the view that copyright is paying for the discovery and publishing of new works, then consumers paying monopoly prices for 70 years or more is a bad idea. By far the majority of works are commercially dead 1 year after being published. The publishers tend to make their money from the remaining 1%. They might last five years. Very, very few last 20. I don't see how copyright lasting beyond 20 years can be justified with anything other than: "because of the good work he did 20 years ago, he deserves to be paid for sitting on his arse for the rest of his life". In reality, he didn't sit on his arse - he donated to a few politicians - but the outcome is almost the same.